The invention relates to the field of aquaculture. More precisely, it concerns a feeding process for aquatic animals, such as fish. More precisely still, it concerns a process for adjusting the supply of feed to these aquatic animals, as a function of their food requirements.
Several types of processes aimed at regulating the supply of feed to fish as a function of their requirements are already known.
According to one of these types, the dispensing of feed is carried out in accordance with rationing tables or charts, which indicate the food requirements of the fish. However, this type of method does not take into account the variations in the food-related behavior of the fish which may depend on numerous factors, such as the temperature, their state of stress, the oxygen content of the water, etc.
According to a second type, the dispensing of food is based on the demand of the fish by virtue of a system invoked directly by the latter when it is hungry, for example by snout blows on a tactile rod. However, the invoking of the tactile rod may occur through play or by accident related to the considerable density of fish in the vicinity of the rod.
According to a third type, the farmers determine by visual observation whether or not the fish are feeding and condition the dispensing of feed on this observation. However, it is not easy to determine visually whether the fish is eating, for several reasons:
firstly the large number of fish per tank sometimes prevents sight of the pellets in the water;
the quality of the water is not always the same: once the water becomes hazy it is very difficult to observe the fish;
in the case of benthic fish, that is to say fish which tend to remain on the bottom, they do not always come to the surface to take the pellets.
According to a fourth type, described by document WO/92 12 628 A, the monitoring of the feeding of fish is carried out by virtue of a sonar with echo on the particles of feed falling below a surface zone and then regarded as not ingested by the fish. This system can only be used for surface-feeding fish.
Moreover, it requires a water height of several meters, this being scarcely compatible with the use of processes of this type in artificial concrete tanks.
According to a fifth type, described by document WO 96/15 663, the monitoring of the feeding of fish is also carried out by virtue of a sonar with echo on the particles of feed, with measurement of the Doppler effect of the sinking food particles.
According to a sixth type described by the document Database WPI, XP 00209 7799, the monitoring of the feeding of fish is carried out by virtue of a measurement of the swimming activity of the fish (excitation and acceleration so as to catch the food, but which may however not correspond solely to feeding activity). This activity measurable between 100 and 1000 Hz does not always make it possible to circumvent spurious noise, in particular in an artificial environment and/or when using pellets rather than soft food.
An aim of the invention is to provide a process for tailoring the dispensing of food to fish, to its actual consumption by the fish, which does not exhibit the drawbacks of the prior art processes mentioned above.
This aim is achieved by virtue of a process for feeding aquatic animals comprising a step of dispensing feed, characterized in that it furthermore comprises a step of slaving the dispensing of feed to the measurement of an acoustic signal characteristic of the food uptake, that is to say, emitted by these animals and corresponding to their ingestion or attempted ingestion of food.
Such a food uptake signal indicates that the fish are actually feeding. The measurement of this signal, for example the measurement of its amplitude, gives a high result when numerous fish are feeding. The result of this measurement decreases when the feeding fish are less numerous.
The slaving of the dispensing of feed to the result of this measurement therefore makes it possible to tailor the dispensing to the actual requirements and thus to avoid waste, doing so without penalizing the demand expressed by the fish.
The process according to the invention exhibits, as compared with the prior art, the following advantages:
it is based solely on the noise of aspiration of a food pellet by the fish; it is therefore a transient emission source formed of a series of brief pulses (5 to 10 ms) whose number is proportional to the number of fish seizing pellets; this aspiration noise which may be likened to a crackling, excites a very wide frequency band from 1000 to 20,000 Hz, or even beyond;
it uses the frequency band from 6 to 9 kHz as the active listening band; this choice makes it possible to circumvent two types of sound pollution frequent in breeding farms: the noise from the surroundings of a concrete tank breeding farm (aerators, pumps, overflows, etc.) and the impact noise of the pellet on the surface of the water;
it is therefore adapted to concrete tank farming systems and to all species which capture their prey by aspiration; and
it avoids recourse to listening to swimming noises since they are practically indiscernible under intensive farming conditions on land, and more generally, since they are not strictly indicators of an actual food uptake.
Other aspects, aims and advantages will become apparent on reading the detailed description which follows. The invention will also be better understood with the aid of the drawings in which: